JavaScript Data Types

JavaScript variables can hold many data types: numbers, strings, objects and more:

var length = 16;                               // Number

var lastName = "Johnson";                      // String

var x = {firstName:"John", lastName:"Doe"};    // Object

The Concept of Data Types

In programming, data types is an important concept.

To be able to operate on variables, it is important to know something about the type.

Without data types, a computer cannot safely solve this:

var x = 16 + "Volvo";

Does it make any sense to add "Volvo" to sixteen? Will it produce an error or will it produce a result?

JavaScript will treat the example above as:

var x = "16" + "Volvo";

When adding a number and a string, JavaScript will treat the number as a string.

Example

var x = 16 + "Volvo";

Example

var x = "Volvo" + 16;

JavaScript evaluates expressions from left to right. Different sequences can produce different results:

JavaScript:

var x = 16 + 4 + "Volvo";

Result:

20Volvo

JavaScript:

var x = "Volvo" + 16 + 4;

Result:

Volvo164